JPH06165260A - Signal converter - Google Patents

Abstract

PURPOSE:To provide a reset circuit by simple constitution by connecting a reset voltage lower than input signals at normal time when a unidirectional semiconductor element is serially connected parallelly to an input signal line. CONSTITUTION:This converter is provided with an optical composite element 5 and the reset circuit 4 by a constant voltage source and the unidirectional semiconductor element. The light emitting element part of the optical composite element 5 is inserted to an output line, a light receiving element part is inserted to the input signal line and the reset circuit 4 of the constant voltage source and the unidirectional semiconductor element is parallelly connected to the input signal line. Then, at the normal time, since the input signals higher then the reset voltage, the direction of a current is reversed for the unidirectional semiconductor element and the reset voltage Vres is cut off. Also, at the time of opening an output circuit, the input signals lower than the reset voltage, the direction of the current is in a forward direction for the unidirection semiconductor element and the reset signals are supplied. Thus, the reset circuit can be realized by the simple constitution using the unidirectional semiconductor element.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an industrial electronic device intended for signal insulation, and more particularly to a signal converter for isolating current signals.

[0002]

2. Description of the Related Art As a unified process signal in process measurement control, a DC voltage signal of 1 to 5 VDC or a DC current signal of 4 to 20 mA is used.

The current signal as the process signal is suitable for long-distance transmission and is generally used as a signal for directly driving an operating end such as a valve or a solenoid valve. Therefore, the disconnection abnormality of the current signal line directly leads to the operation abnormality of the operating end. Therefore, it is necessary to monitor the open abnormality of the current signal line and feed back the readback signal to the host computer to control the operating end on the safe side.

An example of what is known as open circuit abnormality monitoring of a current signal circuit will be described below with reference to FIG.

In FIG. 2, CPU is a host computer, Is is a current signal source for outputting a process current signal Ii, Ro is a load (operating end) to be connected, R is an open abnormality detection resistor, and both ends of the resistor R are generated. Vr is a readback signal to the host computer, and Vco is a control signal to the operating end.

In a steady state, the current signal source Is supplies the process current signal Ii to the load Ro, and at the both ends of the open abnormality detection resistor R, the readback signal Vr is given as a formula 1.
The voltage shown in is generated.

[0007]

Vr = R × Ii (Equation 1) Next, when the current closed circuit is opened for some reason,
Since Ii = 0, the number 1 becomes Vr = 0.

That is, when the value of the readback signal Vr becomes less than a certain value (it varies depending on the current value in the steady state), it is determined that there is an abnormality in the current closed circuit.
The CPU judges and controls the operating end to the safe side by the control signal Vco.

Generally, in the process control, the current signal source Is shown in FIG. 2 and the operating end of the computer CPU and the valve are often separated from each other, so that the reference potentials do not match and noise is prevented. Insulation is often required.

To this end, it is known to insert a signal converter for insulation between the operating end side and the host computer side.

Hereinafter, the open abnormality monitoring of the current closed circuit in the case of using the conventional signal converter with the output open circuit detection function will be described with reference to FIG.

In FIG. 3, the same parts as those in FIG. 2 are represented by the same symbols.

First, in the steady state, the input current Ii from the current signal source Is is input to the signal converter 1 through the open abnormality detection resistor R and the light receiving element section of the optical composite element 5 (ON in the steady state). It flows into the resistor Ri. Here, the input current Ii is converted into the voltage signal Vri as shown in Equation 2.

[0014]

Vri = Ii × Ri (Equation 2) The Vri connected in parallel via R1 and R2, respectively.
And a reset signal Vres which is a constant voltage source
By using P1 and resistors R1 to R4, the voltage is applied to the non-inverting input terminal of the operational amplifier OP1 of the reset circuit 4 which constitutes the adder, and the addition is performed. Here, in the steady state, the light receiving element portion of the optical composite element 6 is also ON, so the reset signal Vres is grounded and Vres = 0. Therefore, the output of the operational amplifier OP1 becomes Vri. here,
The resistor R5 is a current limiting resistor when the reset signal is grounded.

The output Vri of the OP1 is insulated by the insulation circuit 2, converted again into the current output signal Io via the voltage-current conversion circuit 3, and supplied to the load Ro. The light output element Io of the optical composite element 5 and the optical composite element 6 inserted in the output signal line is turned on by the current output signal Io.

Next, it is assumed that an opening abnormality occurs at point A of the output circuit shown in FIG.

When the point A is opened, the output current Io becomes Io.
= 0, so the light-emitting elements of the optical composite elements 5 and 6 are off
Becomes Therefore, the light receiving element portion of the optical composite element 5 is O
Since it becomes FF, the input signal circuit is opened, and the readback signal Vr = 0 as described with reference to FIG. 2, there is an abnormality in the output current closed circuit and the host computer C
PU judges and loads Ro (valve) by control signal Vco
Control to the safe side. Further, the light receiving element portion of the optical composite element 6 is also turned off, and the reset signal Vres is applied to the non-inverting input terminal of the operational amplifier OP1 via the resistor R2. Here, when the output end is opened, V
Since the input terminal of ri is also opened, the input current Ii = 0
And Vri = 0. Therefore, the output of OP1 forming the adder becomes Vres.

As a result, when the open circuit abnormality of the output circuit is improved, the output Vres of the OP1 is converted into a current signal through the insulating circuit 2 and the voltage-current conversion circuit 3 and inserted into the output signal line. Further, the light emitting element portions of the optical composite element 5 and the optical composite element 6 are turned on, the light receiving element portions of the optical composite element 5 and the optical composite element 6 are turned on, and the input circuit is closed. As a result, the input signal Ii is supplied again to the input resistor Ri. Further, since the light receiving element section of the optical composite element 6 of the reset circuit 4 is also turned on, Vres supplied to the adder is grounded and Vres = 0.

Therefore, only the input signal Vri is applied to the non-inverting input terminal of the operational amplifier OP1, converted into the output current Io through the insulating circuit 2 and the voltage-current circuit 3, and supplied to the load Ro. It As described above, the steady state is restored.

When the power of the signal converter is turned on, the input current Ii from the current signal source Is passes through the light receiving element portion of the optical composite element and the open abnormality detection resistor R, and the input resistance Ri of the signal converter 1. However, since the light emitting element portion of the optical composite element 5 inserted in the output circuit is in the OFF state because the input signal is not applied, the light receiving element portion of the optical composite element 5 is turned off. It remains in the state. Therefore,
The input circuit remains open and does not shift to steady operation. Therefore, also at the first startup, as in the case where the opening abnormality at the output end is improved,
By the reset voltage Vres of the reset circuit 4, the light-emitting element portions of the optical composite element 5 and the optical composite element 6 inserted in the output signal line are turned on, the input circuit is closed, and the operation shifts to the steady operation.

With the above configuration, the open abnormality of the output end is detected.

[0022]

The structure shown in the conventional example has the following problems.

(1) Although the reset circuit 4 is an unnecessary circuit in a steady state, its structure is complicated.

(2) Since the input signal in the steady state passes through the unnecessary operational amplifier OP1 of the reset circuit, it is necessary to consider the influence on the conversion accuracy such as offset error.

(3) Since the light emitting element portions of the optical composite elements 5 and 6 used for detecting the output end opening have a voltage drop themselves, the allowable load resistance Ro becomes low.

Here, the voltage that the output current source can output is V
p, the voltage drop of the optical composite element 5 is Vf5, and the voltage drop of the optical composite element 6 is Vf6, the load resistance Ro is given by Equation 3.

[0027]

[Equation 3]

[0028]

The essential point of the present invention is that, in the configuration of the reset circuit 4, a reset voltage Vres lower than the input signal in the steady state connected in series with the unidirectional semiconductor element is applied to the input signal line. The point is that they are connected in parallel.

[0029]

In other words, in a steady state, the input signal> the reset voltage, so that the unidirectional semiconductor element has a reverse current direction, and the reset voltage Vres is cut off.

Further, when the output circuit is opened, the input signal becomes smaller than the reset voltage, and the unidirectional semiconductor element is supplied with the reset signal because the current flows in the forward direction. With the above configuration, a simple reset circuit can be realized.

[0031]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A signal converter with an output end open detection function according to the present invention will be described in detail below with reference to the embodiment of FIG.

FIG. 1 shows an open circuit abnormality monitoring of an output current circuit using a signal converter with an output terminal open detection function according to the present invention. Here, the current signal source Is uses DC4 to 20 mA which is a standard unified signal in process control. Further, the input resistance Ri is set to 250Ω (Vr at steady state)
i = DC1 to 5V), and the reset voltage Vres is set to Vres = 0.5V, which is lower than the input signal Vri in the steady state, as shown in the means for solving the above problems.

First, in a steady state, the light receiving element portion of the optical composite element 5 is ON and the input circuit is closed, so that the input current Ii = DC4 to 20 mA flows into the input resistance Ri and the voltage signal Vri = DC1 to DC1. Converted to 5V. As a result, Vri> Vres and the direction of the current of the unidirectional semiconductor element D1 is reversed, so that the reset signal Vres is disconnected. As a result, the input signal D
C1 to 5V is applied, and the voltage-current conversion circuit 3 converts the current output signal Io = DC4 to 20mA to load R.
supplied to the o. It should be noted that the current output signal Io causes the light-emitting element portion of the optical composite element 5 inserted in the output signal line to be turned on.
It is N.

If the point A of the output circuit of the signal converter is opened, the output current Io becomes 0 mA. As a result, since the light emitting element portion of the optical composite element 5 is turned off, the light receiving element portion of the optical composite element 5 is also turned off,
Open the input circuit. Therefore, the voltage readback signal Vr = across the output end open detection resistor R inserted in the input end
It becomes 0V, and the computer CPU judges that there is an open abnormality,
The control signal Vco controls the operating end Ro to the safe side. On the other hand, Vri =
Since it becomes 0V, Vri <Vres, so that the reset voltage Vres is applied to the insulation circuit 2 as in the case of power supply startup, and the voltage-current conversion circuit 3 tries to output the output current Io = 2mA according to the reset signal Vres. The standby state for waiting for recovery from the open abnormality at point A is set.

When the open abnormal condition at the point A is improved and the output circuit is connected, the light emitting element portion of the optical composite element 5 is turned on by the output current Io = 2 mA due to the reset signal Vres, and the light is accordingly emitted. The light receiving element portion of the composite element 5 is turned on and the input end is closed. Therefore, the input current I
i = DC4 to 20 mA flows into the input resistance Ri and is converted into a voltage signal Vri = DC1 to 5V. From this, Vri> Vres again, and the direction of the current of the unidirectional semiconductor element D1 is reversed, so that the reset signal Vres is disconnected. As a result, the input signal DC is applied to the insulation circuit 2.
1 to 5 V is applied, and the voltage-current conversion circuit 3 converts the current output signal Io = DC4 to 20 mA to load Ro.
And is returned to the normal operation.

When the power of the signal converter is turned on, Vri = 0 (V) because the input circuit remains open, but since the reset voltage Vres = 0.5 (V) is activated, Vri becomes Vri. <Vres, and the reset voltage is applied to the insulating circuit 2 via the unidirectional semiconductor element D1, and the voltage −
The current conversion circuit 3 converts the current output signal Io to 2 (mA). By the current output signal, the light emitting element portion of the output end open detection optical composite element 5 is turned on, and accordingly, the light receiving element portion of the optical composite element 5 is turned on to close the input end. Therefore, the input current Ii = DC4 to 20 mA flows into the input resistor Ri and is converted into a voltage signal Vri = DC1 to 5V. As a result, Vri> Vres, and the direction of the current of the unidirectional semiconductor element D1 is reversed, so that the reset signal Vres is disconnected. As a result, the input signals DC1 to 5V are applied to the insulation circuit 2, converted into the current output signal Io = DC4 to 20mA by the voltage-current conversion circuit 3, and supplied to the load Ro. As described above, the signal converter enters the normal operation.

As described above, the signal converter with the output end opening detection function is configured.

In this embodiment, the optical semiconductor element is used to detect the open abnormality of the output circuit and open the input circuit. However, the present invention is not limited to this. Any element and structure that can control the input / output circuit by insulating it, such as a relay, can be applied.

[0039]

According to the present invention, the signal converter with the output end open detection function can be realized with a simpler structure than the structure shown in the conventional example.

Further, by adopting a simple reset circuit configuration using a unidirectional semiconductor element, an operational amplifier which is conventionally inserted in an input signal line is not required, and there is no influence on instrument accuracy.

Further, since the reset circuit according to the present invention does not require the output end open detection signal by the optical composite element,
The optical composite element 6 conventionally inserted in the output signal line is unnecessary. Therefore, the allowable value of the load Ro can be further increased by the amount of the voltage drop of the light emitting element section of the optical composite element. Here, the value of the load Ro shown in (Equation 3) is (Equation 4)
Becomes

[0042]

[Equation 4]

As described above, according to the present invention, it is possible to realize a signal converter with an output end open detection function which can solve all the problems in the conventional example with a simple structure and at low cost.

[Brief description of drawings]

FIG. 1 is a diagram showing an open abnormality monitoring of a current closed circuit using a signal converter with an output end open detection function according to the present invention.

FIG. 2 is a diagram showing a known example of open abnormality monitoring of a current closed circuit.

FIG. 3 is a diagram showing an open abnormality monitoring of a current closed circuit using a conventional signal converter with an output open circuit detection function.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Signal converter, 2 ... Insulation circuit, 3 ... Voltage-current conversion circuit, 4 ... Reset circuit, 5 ... Optical composite element (for opening and closing an input end), 6 ... Optical composite element (for reset circuit).

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshihiro Yanagihara 500 Mt. Yamayama, Uchihara-cho, Higashi-Ibaraki-gun, Ibaraki Prefecture, 500 Hitachi Naka Electronics Co., Ltd.

Claims (2)

[Claims] 1. A current-voltage conversion circuit for converting a current signal into a voltage signal, an insulating circuit for insulating between input and output signals, and a voltage-current for converting the insulated voltage signal into a current signal again and outputting the current signal. A signal converter having a conversion circuit, comprising an optical composite element and a series circuit of a constant voltage source and a unidirectional semiconductor element, wherein the light emitting element section of the optical composite element is an output signal line, and a light receiving element The element unit is inserted into each input signal line, the series circuit of the constant voltage source and the unidirectional semiconductor element is connected in parallel to the input signal line, and when the output circuit is opened, the input circuit is connected by the optical composite element. A signal conversion device, characterized in that, when the output circuit is closed while being opened, the optical composite device is driven by the constant voltage source and the unidirectional semiconductor device to close the input circuit. 2. An input / output circuit such as a relay or a pulse transformer is insulated instead of an optical composite element for detecting an open circuit abnormality of an output circuit and opening an input circuit according to claim 1.
A signal converter characterized by performing open circuit abnormality detection of the output circuit using a controllable structure.